This invention generally relates to the field of paper making, and more specifically, to a tissue with strikethrough resistance.
A user often uses more tissue than necessary, especially after urination. The user often uses excessive tissue to prevent urine or other liquid from passing from one side of the tissue to the opposite side, next to the user""s hand. Using excessive tissue results in tissue waste, which expends economic resources and degrades the environment.
Accordingly, a tissue product that has a relatively long absorbency rate to delay liquid from saturating the tissue and pass from one side of the tissue to the other, would be desirable. In addition, such a tissue product would have a reasonable absorbency capacity to absorb liquid. The tissue product would also, ideally, break up relatively rapidly after being immersed in liquid. Such a tissue product having these attributes would reduce tissue consumption waste while addressing economic and environmental issues.
As used herein, the term xe2x80x9crepellant agentxe2x80x9d refers to an agent that resists absorption of a liquid, desirably an aqueous liquid. The repellant agent may repel liquids by filling interstitial voids in the fibrous structure of a tissue or by coating individual fibers thereby preventing liquids from being absorbed by and passing through the fibers to the interior of the fibrous structure, as measured by test procedure ASTM D 779-94. When repellant action is accomplished, the contact angle at the fiber surface is about 90 degrees or greater, as measured by test procedure ASTM D 5725-95 or TAPPI Test Method T-458. The repellant agent is preferably a hydrophobic chemical, and may include other materials, such as sizing agents, waxes, and latexes, may also be included. When included, the amounts of the other materials comprise less than 20% of the total composition of the repellant agent, preferably less than 10% of the total composition of the repellant agent, and more preferably less than 5% of the total composition of the repellant agent, and even more preferably less than 2% of the total composition of the repellant agent. By way of example only, a suitable repellant agent is a hydrophobic chemical having a primary composition comprising mono- and distearamides of aminoethylethanolamine, such as:
C17H35CONHCH2CH2NHCH2CH2OH
or
(C17H35C0)2NCH2CH2NHCH2CH20H
One such agent is sold under the trade name REACTOPAQUE (hereinafter xe2x80x9cROxe2x80x9d) by Sequa Chemicals, Inc., at One Sequa Dr., Chester, S.C. 29706. The amount of repellant agent added to the fibers may be from about 2 to about 20 pounds of active ingredient per ton of fiber, more specifically from about 3 to about 15 pounds of active ingredient per ton of fiber, still more specifically, from about 4 to about 12 pounds of active ingredient per ton of fiber, and even more specifically, from about 6 to about 10 pounds of active ingredient per ton of fiber.
As used herein, the term xe2x80x9clatexxe2x80x9d refers to a colloidal water dispersion of high polymers from sources related to natural rubber, such as Hevea tree sap, or of synthetic high polymers that resemble natural rubber. Synthetic latexes may be made by emulsion polymerization techniques from styrene-butadiene copolymer, acrylate resins, polyvinyl acetate, and other materials.
As used herein, the term xe2x80x9cwaxxe2x80x9d refers to aqueous emulsions of small particles held in suspension by emulsifying agents and may include materials such as paraffin waxes, microcrystalline wax, or other waxes.
As used herein, the term xe2x80x9csizing agentxe2x80x9d refers to any chemical inhibiting liquid penetration to cellulosic fiber structures. Suitable sizing agents are disclosed in a test entitled, xe2x80x9cPapermaking and Paper Board Makingxe2x80x9dxe2x80x9d second edition, Volume III, edited by R. G. Macdonald, and J. N. Franklin, which is hereby incorporated by reference herein.
As used herein, the term xe2x80x9cstrikethrough resistancexe2x80x9d refers to a characteristic of a tissue product which slows or impedes the movement of liquid from one surface of the tissue to the opposite surface. Such a tissue product has a relatively high absorbency rate, i.e., of at least 10 seconds, but still has a reasonable gms/gms absorbency capacity. For example, a tissue product having a basis weight of about 10 gsm to about 35 gsm, and more desirably about 27 gsm, may have an absorbency rate desirably between about 10 seconds to about 430 seconds, and more desirably between about 10 seconds and about 30 seconds, and an absorbency capacity desirably between about 7 gms/gms to about 13 gms/gms. In another example, a tissue product having a basis weight of about 10 gsm to about 45 gsm, and more desirably, about 33 gsm (each ply having a basis weight of about 16 gsm), may have an absorbency rate desirably between about 10 seconds to about 430 seconds, and still more desirably between about 10 seconds to about 30 seconds, and may have an absorbency capacity desirably between about 7 gms/gms to about 13 gms/gms.
As used herein, the term xe2x80x9clayerxe2x80x9d refers to a single thickness, course, stratum, or fold that may lay or lie on its own, or, that may lay or lie over or under another.
As used herein, the term xe2x80x9cplyxe2x80x9d refers to a material having one or more layers. An exemplary toilet tissue product having a single ply structure is illustrated in FIGS. 1-2; an exemplary toilet tissue product having a two-ply structure is depicted in FIG. 3.
As used herein, the term xe2x80x9ccellulosic materialxe2x80x9d refers to material that may be prepared from cellulose fibers from synthetic sources or natural sources, such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and begasse. The cellulose fibers may be modified by various treatments such as, for example, thermal, chemical, and/or mechanical treatments. It is contemplated that reconstituted and/or synthetic cellulose fibers maybe used and/or blended with other cellulose fibers of the fibrous cellulosic material. Desirably, no synthetic fibers are woven into the cellulosic fibers.
As used herein, the term xe2x80x9cpulpxe2x80x9d refers to cellulosic fibrous material from sources such as woody and non-woody plants. Woody plants include, for example, deciduous and confierous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse. Pulp may be modified by various treatments such as, for example, thermal, chemical and/or mechanical treatments. Desirably, no synthetic fibers are woven into the pulp fibers.
As used herein, the term xe2x80x9cbasis weightxe2x80x9d (hereinafter may be referred to as xe2x80x9cBWxe2x80x9d) is the weight per unit area of a sample and may be reported as gram-force per meter squared. The basis weight may be measured using test procedure ASTM D 3776-96 or TAPPI Test Method T-220.
As used herein, the term xe2x80x9cwet strength agentxe2x80x9d refers to a xe2x80x9ctemporaryxe2x80x9d wet strength agent. For purposes of differentiating permanent from temporary wet strength, permanent will be defined as those resins which, when incorporated into paper or tissue products, will provide a product that retains more than 50% of its original wet strength after exposure to water for a period of at least five minutes. Temporary wet strength agents are those which show less than 50% of their original wet strength after exposure to water for five minutes. Only temporary wet strength agents find application in the present invention. The amount of wet strength agent added to the pulp fibers can be at least about 0.1 dry weight percent, more specifically from about 0.2 dry weight percent or greater, and still more specifically from about 0.1 to about 3.0 dry weight percent based on the dry weight of the fibers.
The temporary wet strength resins that can be used in connection with this invention include, but are not limited to, those resins that have been developed by American Cyanamid and are marketed under the name PAREZ 631-NC (now available from Cytec Industries, West Paterson, N.J.). This and similar resins are described in U.S. Pat. No. 3,556,932 to Cosica et al. and U.S. Pat. No. 3,556,933 to Williams et al. Other temporary wet strength agents that should find application in this invention include a dry strength starch such as those available from National Starch and marketed under the tradename REDI-BOND 2005. It is believed that these and related starches are covered by U.S. Pat. No. 4,675,394 to Solarek et al. Derivatized dialdehyde starches, such as described in Japanese Kokai Tokkyo Koho JP 03,185,197, should also find application as useful materials for providing temporary wet strength. It is expected that other temporary wet strength materials such as those described in U.S. Pat. Nos. 4,981,557; 5,008,344 and 5,085,736 to Bjorkquist would be of use in this invention. With respect to the classes and the types of wet strength resins listed, it should be understood that this listing is simply to provide examples and that this is neither meant to exclude other types of temporary wet strength resins, nor is it meant to limit the scope of this invention.
The term xe2x80x9cdebonderxe2x80x9d or xe2x80x9cdebonder agentxe2x80x9d refers to any chemical that can be incorporated into paper products such as tissue to prevent or disrupt interfiber or intrafiber hydrogen bonding. Desirable chemical debonder agents include fatty chain quaternary ammonium salts (QAS) made by Eka Nobel, Inc. Marietta, Ga., or compounds made by Witco Corp., Melrose Park, Ill. One debonder agent from Witco Corp. often used is C-6027, an imidazoline QAS. Other QAS compounds from Witco Corp. which may be used include ADOGEN 444, a cethyl trimethyl QAS, VARISOFT 3690PG, an imadazoline QAS, or AROSURF PA 801, a blended QAS.
As used herein, xe2x80x9cAbsorbent Capacityxe2x80x9d refers to the amount of distilled water that an initially 4 by 4-inch (+/xe2x88x920.01 in.) of cellulose material can absorb while in contact with a pool 2 in. deep of room-temperature (23+/xe2x88x922xc2x0 C.) distilled water for 3 minutes +/xe2x88x925 seconds in a standard laboratory atmosphere of 23+/xe2x88x921xc2x0 C. and 50+/xe2x88x922% RH and still retain after being removed from contact with liquid water and being clamped by a one-point clamp to drain for 3 minutes +/xe2x88x925 seconds. Absorbent capacity is expressed as grams of water held per gram of dry fiber, as measured to the nearest 0.01 g.
As used herein, the xe2x80x9cAbsorbency Ratexe2x80x9d is a measure of the water repellency imparted to the tissue by the repellant agent. The Absorbency Rate is the time it takes for a product to be thoroughly saturated in distilled water. To measure the Absorbency Rate, samples are prepared as 3 inch squares composed of 2 different product sheets. In this instance the sheets in Examples 1A to 1E are from one product having a 1-ply sheets having a single blended layer; the sheets from Examples 2A to 2E are from a product having two 2-ply sheets having two identical layers. Six (6) sheets are conditioned by placing them in an oven at 105xc2x0 C. for 5 minutes. The samples are draped over the top of a 250 ml beaker and covered with a 5 by 5 in. template having a 2 in. diameter opening. An amount of distilled water is dispensed from a pipette (0.01 cc for 1-ply samples; 0.1 cc for 2-ply samples) positioned 1 in. above the sample and at a right angle to the sample, and a timer accurate and readable to 0.1 sec. is started when the water first contacts the sample. The timer is stopped when the fluid is completely absorbed. At least six samples are tested; two readings are taken from one side of the sample(s), and two readings are taken from the opposite side. The end point of timing is reached when the fluid is absorbed to the point where light is not reflecting from the surface of the water on the sample. Results are recorded to the nearest 0.1 sec. The absorbency rate is the average of the four absorbency readings (the two on one side and the two on the other side of the sample). A minimum of six samples are tested and the test results are averaged. All tests are conducted in a laboratory atmosphere of 23+/xe2x88x921xc2x0 C. and 50+/xe2x88x922% RH, and all samples are stored under these conditions for at least 4 hours before testing.
As used herein, xe2x80x9cadditivesxe2x80x9d refers to any agent of substance incorporated in or sprayed on pulped fibers during the papermaking process, such as, but not by way of limitation, sizing agent(s), wax(es), latex(es), (temporary) wet strength agent(s), and so forth.
As used herein, the term xe2x80x9cmachine directionxe2x80x9d is the direction of a material parallel to its forward direction during processing.
As used herein, the term xe2x80x9ccross directionxe2x80x9d is the direction of a material perpendicular to its machine direction.
As used herein, the term xe2x80x9cmachine direction tensilexe2x80x9d (hereinafter may be referred to as xe2x80x9cMDTxe2x80x9d) is the breaking force in the machine direction required to rupture a one or three inch width specimen and may be reported as gram-force.
As used herein, the term xe2x80x9ccross direction tensilexe2x80x9d (hereinafter may be referred to as xe2x80x9cCDTxe2x80x9d) is the breaking force in the cross direction required to rupture a one or three inch specimen and may be reported as gram-force.
As used herein, the term xe2x80x9cGMTxe2x80x9d refers to geometric mean tensile strength, which is the square root of the product of the machine direction tensile strength and the cross-machine direction tensile strength of the web. Unless otherwise indicated, the term xe2x80x9ctensile strengthxe2x80x9d means xe2x80x9cgeometric mean tensile strength.xe2x80x9d Tensile strengths are measured using a standard Instron tensile tester having a 2-inch jaw span using 3-inch wide strips of tissue under TAPPI conditions (23+/xe2x88x921xc2x0 C. and 50+/xe2x88x922% RH), with the tensile test run at a crosshead speed of 10 (+/xe2x88x920.4) in/min. after maintaining the sample under TAPPI conditions for 4 hours before testing.
A toilet tissue product is provided, which comprises a cellulosic ply having at least one layer incorporating a repellant agent and a debonder. The repellant agent and the debonder are each dispersed substantially uniformly throughout the layer. The layer is configured to provide a substantially homogeneous structure having an increased absorbency rate of at least 10 seconds with a reduced dry tensile strength to provide rapid dissolution of the layer when it is immersed in liquid.
A method for making a toilet tissue product in a wet-end stock system including a chest and a headbox is also provided. An aqueous suspension comprising papermaking fibers is provided. A repellant agent and a debonder are added to the aqueous suspension of papermaking fibers prior to forming a web. The repellant agent and the debonder are substantially uniformly dispersed throughout the aqueous suspension of papermaking fibers. The aqueous suspension of papermaking fibers are then deposited onto a forming fabric to form a web having a substantially homogeneous structure. The web is dried to form a toilet tissue product having an increased absorbency rate of at least 10 seconds with a reduced dry tensile strength.